Conventionally, unmanned aircrafts (hereinafter also referred to as “UAVs (unmanned aerial vehicles)”) called “drones” have been used for various applications such as military applications and crop-dusting. In particular, with the recent reduction in size and increase in output of batteries, small-sized unmanned aircrafts using an electric motor as the power source have been developed (e.g., see Non-Patent Documents 1 and 2). The small-sized unmanned aircrafts are simple to operate, and thus are quickly becoming widespread.
In addition, an unmanned aircraft includes a GPS (Global Positioning System) receiver, and can specify its own position. Accordingly, autopilot by which flight is carried out along a set path has been implemented for the unmanned aircraft, leading to a further increase in the applications of the unmanned aircraft.